An electric power conversion apparatus such as a converter or an inverter is used as an electric power source for an electric motor in general industrial fields. In the electric power conversion apparatus such as the converter or the inverter, electric power conversion is performed by supplying/interrupting electric power using a semiconductor device such as an IGBT (insulated gate bipolar transistor), a thyristor, a transistor, or a diode. Because power loss in the semiconductor device results in heat generation, when the semiconductor device reaches a higher temperature due to heat generated with power loss, its normal operation cannot be maintained, or its conversion efficiency is decreased. It is important for the electric power conversion apparatus that the semiconductor device is cooled to be within a predetermined temperature range. Here, in some cases, an IPM (intelligent power module) is also used in which the semiconductor device is modularized integrally including its driving circuit.
In a conventional electric power conversion apparatus, a system has been practically used in which the semiconductor device is cooled using a heat pipe. The heat pipe has a structure in which coolant is sealed in a tube stood in the vertical orientation; a target to be cooled is contacted with a lower portion of the tube; and a fin or like heat-dissipative structure is provided in its upper portion. The coolant sealed in the tube is vaporized in the lower portion by the heat received from the target to be cooled. The vaporized coolant moves toward the upper portion of the tube, and then returns to the liquid state with losing its heat at the upper portion of the tube, and thereafter the liquid-state coolant, after flowing along the inside wall of the tube, is accumulated at the lower portion. The accumulated coolant is again vaporized. As described above, in the heat pipe, by vaporizing the coolant, the heat is transferred from the lower to the upper portion, and is then dissipated from the upper portion to the outside, whereby the target to be cooled that is contacted with the lower portion is cooled.
In an electric power conversion apparatus using a heat pipe, a circuit board on which a semiconductor device that generates heat is mounted is horizontally arranged so that the semiconductor device faces downward, whereby the heat pipe is placed to contact with the upward-facing bottom face of the circuit board (for example, refer to Patent Document 1).
An electric power conversion apparatus for an electric rolling stock has also been practically used, which includes a heat-receiving plate having a flow channel for flowing cooling liquid therethrough, to which a semiconductor device is attached, a heat exchanger for exchanging heat between the cooling liquid from the heat-receiving plate and the air, a pump for circulating the cooling liquid between the heat-receiving plate and the heat exchanger, and a blowing means for blowing cooling wind to the heat exchanger, and in which plural sets of the heat-receiving plates, the heat exchangers, the pumps, and the blowing means are collinearly arranged perpendicularly to the longitudinal orientation of the car body. The blowing means and the heat-receiving plate face approximately in parallel with each other, while the heat exchanger and the heat-receiving plate are positioned perpendicularly to each other (for example, refer to Patent Document 2).
[Patent Document 1]    Japanese Laid-Open Patent Publication No. 2002-134670
[Patent Document 2]    Japanese Laid-Open Patent Publication No. 1997-246767